Upbound input/output expansion request and response processing in a PCIe architecture

ABSTRACT

Embodiments of the invention relate to upbound input/output expansion requests and response processing in a PCIE architecture. A first request to perform an operation on a host system is intitiated. The first request is formatted for the first protocol and includes data that is required in order to process the first request. A second request is created in response to the first request, the second request includes a header and is formatted according to the second protocol. The data required to process the first request in the header of the second request is stored, and the second request is sent to the host system.

BACKGROUND

This invention relates generally to processor input/output (I/O)interfacing within a computing environment, and more particularly toupbound processing of I/O expansion requests and responses over a PCIebus and switch architecture.

PCIe is a component level interconnect standard that defines abi-directional communication protocol for transactions between I/Oadapters and host systems. PCIe communications are encapsulated inpackets according to the PCIe standard for transmission on a PCIe bus.Packets originating at I/O adapters and ending at host systems arereferred to as upbound packets. Packets originating at host systems andterminating at I/O adapters are referred to as downbound packets. PCIetransactions include a request packet and, if required, a completionpacket (also referred to herein as a “response packet”) in the oppositedirection. The PCIe topology is based on point-to-point unidirectionallinks that are paired (e.g., one upbound link, one downbound link) toform the PCIe bus. The PCIe standard is maintained and published by thePeripheral Component Interconnect Special Interest Group (PCI-SIG).

One drawback to the use of PCIe is that all I/O adapters connected to aPCIe bus are required to operate within the parameters defined in thePCIe standard (i.e., they are PCIe compatible I/O adapters). The PCIestandard sets rigid constraints on requests and, completions and onpacket packaging and addressing. In some system architectures, forexample the IBM® System z® architecture, there is a need to be able tosupport communications over a PCIe bus between I/O adapters and hostsystems using transactions that are not supported by the PCIe standard.An example is the ability to communicate with non-PCIe compatibleadapters (e.g., I/O expansion adapters), which are typically supportinglegacy systems and applications that may be difficult (due, for exampleto technology issues and/or expense) to convert into the PCIe standard.Thus, while PCIe is suitable for its intended purpose of communicatingwith PCIe compatible adapters, there remains a need for expanding thiscapability to allow PCIe to communicate with non-PCIe compatibleadapters to support legacy systems.

BRIEF SUMMARY

A system for implementing non-standard I/O adapters in a standardizedinput/output (I/O) architecture, the system comprising an I/O adaptercommunicatively coupled to an I/O hub via an I/O bus, the I/O adaptercommunicating in a first protocol, the I/O bus communicating in a secondprotocol different than the first protocol, and the I/O adapterincluding logic for implementing a method comprising initiating a firstrequest to perform an operation on a host system, the first requestformatted for the first protocol and comprising data required to processthe first request, and creating a second request responsive to the firstrequest, the second request comprising a header and formatted accordingto the second protocol, the creating comprising storing the datarequired to process the first request in the header of the secondrequest. The method further comprising sending the second request to thehost system.

A system for implementing non-standard I/O adapters in a standardizedI/O architecture, the system comprising, an I/O adapter communicativelycoupled to an hub via an I/O bus, the I/O adapter including logic forimplementing a method comprising, receiving a request from a requesterto perform an operation on the I/O adapter, the requester requiring acompletion status. The method further comprising performing theoperation resulting in a response, the response comprising thecompletion status, generating a new request in response to theperforming, the new request in a format supported by the I/O bus, andmodifying the header of the new request to include the response. Themethod additionally comprising sending the new request as the completionstatus to the requester.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with advantagesand features, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alikein the several FIGURES:

FIG. 1 depicts a block diagram of a computer system that may beimplemented in an exemplary embodiment;

FIG. 2 a depicts a block diagram of a standard Peripheral ComponentInterconnect Express (PCIe) request header;

FIG. 2 b depicts a block diagram of a standard PCIe completion header;

FIG. 3 depicts a block diagram of an exemplary embodiment ofinput/output (I/O) expansion logic for downbound request and completionprocessing;

FIG. 4 depicts a block diagram of an exemplary embodiment of I/Oexpansion logic for upbound request and completion processing;

FIG. 5 depicts a process flow of an exemplary embodiment of I/Oexpansion logic for processing an upbound request;

FIG. 6 depicts block diagram of a transformed PCIe request header thatmay be implemented by an exemplary embodiment;

FIG. 7 depicts a process flow of an exemplary embodiment of I/Oexpansion logic for processing a upbound response; and

FIG. 8 depicts a block diagram of an exemplary embodiment of atransformed PCIe request header containing an I/O expansion response.

DETAILED DESCRIPTION

An exemplary embodiment of the present invention provides for processingof input/output (I/O) expansion requests and responses in a PeripheralComponent Interconnect Express (PCIe) architecture without requiringmodification of the PCIe bus and PCIe switch infrastructure.

FIG. 1 depicts a computer system 100 that may be implemented by anexemplary embodiment of the present invention. In an embodiment, thecomputer system 100 is a System z® server offered by InternationalBusiness Machines Corporation (IBM®). System z is based on thez/Architecture® offered by IBM. Details regarding the z/Architecture aredescribed in an IBM publication entitled, “z/Architecture Principles ofOperation,” IBM Publication No. SA22-7832-07, February 2009, which ishereby incorporated herein by reference in its entirety.

In an exemplary embodiment, computer system 100 includes one or morecentral processing units (CPUs) 102 coupled to a system memory 104 via amemory controller 106. System memory 104 is accessed when a CPU 102,PCIe adapter 110, or I/O expansion adapter 111 issues a memory request(read or write) that includes an address used to access the systemmemory 104. The address included in the memory request is typically notdirectly usable to access system memory 104, and therefore, it requirestranslation to an address that is directly usable in accessing systemmemory 104. In an embodiment, the address is translated via an addresstranslation mechanism (ATM) 108. In an embodiment, the ATM 108translates the address from a virtual address to a real or absoluteaddress using, for example, dynamic address translation (DAT).

The memory request, including the translated address, is received by thememory controller 106. In an embodiment, the memory controller 106maintains consistency in the system memory 104 and arbitrates betweenrequests for access to the system memory 104 from hardware and softwarecomponents including, but not limited to, the CPUs 102, the PCIeadapters 110, and the I/O expansion adapters 111 known collectively asI/O adapters.

In an exemplary embodiment, the PCIe adapters 110 perform one or morePCIe I/O functions; and the I/O expansion adapters 111 are not PCIecompatible and perform one or more non-PCIe I/O functions. A memoryrequest that is sent from one of the CPUs 102 to the PCIe adapters 110or the I/O expansion adapters 111 (i.e., a downbound memory request) isfirst routed to an I/O hub 112 (e.g., a PCIe hub), which is connected toa PCIe bus 126 (also described herein as an I/O bus). The memory requestis then sent from the PCIe bus 126 to one of the PCIe adapters 110 or toone of the I/O expansion adapters 111 via one or more PCIe switches 114.The PCIe bus 126 and PCIe switches 114 communicate in a standard PCIeformat (or protocol) as is known in the art.

In an exemplary embodiment, the I/O hub 112 includes one or more statemachines, and I/O expansion logic 122 for interpreting and transmittingI/O expansion operations, bi-directionally, between the host system 124and the I/O expansion adapters 111. The host system 124 transmitsrequests to the I/O expansion adapters 111 in a format supported by theI/O expansion adapters 111 but incompatible (i.e. not supported) by thePCIe bus 126 and the PCIe switches 114. The I/O expansion logic 122receives requests and responses from the host system 124 via the hostbus 120 and transforms them into a format supported by the PCIe bus 126.As depicted in FIG. 1, the I/O expansion logic 122 includes bothdownbound expansion logic 128 and upbound expansion logic 130 which areshown as separate logic blocks, however portions or all of the logicwithin these blocks may overlap. The I/O hub 112 depicted in FIG. 1 alsoincludes a root complex 116 that receives request and completions fromone of the PCIe switches 114. Memory requests include an I/O addressthat may need to be translated, and thus, the I/O Hub 112 provides theaddress to an address translation and protection unit (ATP unit) 118.The ATP unit 118 is used to translate, if needed, the I/O address intoto an address directly usable to access system memory 104.

An upbound memory request initiated from one of the PCIe adapters 110 orI/O expansion adapters 111, including the address (translated or initialaddress, if translation is not needed), is provided to the memorycontroller 106 via, for instance, the host bus 120. The memorycontroller 106 performs arbitration and forwards the memory request withthe address to the system memory 104 at the appropriate time to thesystem memory 104.

In an exemplary embodiment, a memory request is initiated by one of thePCIe adapters 110, by one of the I/O expansion adapters 111, or by thehost system 124. In an exemplary embodiment, there are two types ofmemory requests, posted requests and non-posted requests. Non-postedrequests (e.g. memory reads) return a response called a completion thatcontains the requested data and information related to the status of theresult of processing the associated memory request as will be describedin more detail below. Posted transactions (e.g. memory writes) aresimilar to non-posted transactions except that the data is the payloadand posted transactions do not return a completion packet. Therefore,any error that occurs during the posted transaction will be unknown tothe requester. Both posted and non-posted requests flow through the PCIeinfrastructure based on address information contained in their headersas will be described in more detail below.

While PCI defines only Memory Read and Posted Memory Write requests fromthe PCIe adapters 110 to the root complex 116, System z uses severalhigher function requests not defined by the PCI specification. All ofthese requests are various types of atomic requests used for lockingprotocols and bit manipulation.

One request is called Test and Set. This request operates like a memoryread and includes a lock byte and a memory address. If the first byte ofthe target address (8 byte aligned) is zero, the lock byte is writteninto this first byte. The target data, up to 256 bytes in thisimplementation, is returned to the requester. A second request is calledTest and Store. This request operates like a Memory Write with a payloadof up to 256 bytes in this implementation. It differs from a MemoryWrite in that the first byte of the payload is used as a lock byte. Ifthe first byte in the target address is zero, the payload is writteninto the target address. If the first byte in the target address is notzero, the payload is not written into the target address, and a responseis generated indicating that the first target byte was not zero.

Three other requests manipulate bits in memory and one also causes aninterruption. All three operate like Memory Write requests, and allthree include a mask to indicate which target bits should be set orreset. In this implementation, the mask is 8 bytes. The Set Bit Requestsets bits indicated by the mask at the target in memory. The Reset BitRequest resets bits indicated by the mask at the target memory. The SetBit with Interrupt Request first sets bits indicated by the mask at thetarget in memory and then causes an interruption to the host processor.

Turning now to FIGS. 2 a and 2 b, a standard PCIe request and completionheader will be described. A typical PCIe memory request includes aheader, and if the request is a write, it also includes payload data. Atypical PCIe memory completion for a read request includes a header andpayload data. The standard PCIe request header 200 comprises a pluralityof fields. As shown in the embodiment in FIG. 2 a, the first 4 bytes 202of the standard 64 bit address PCIe request header 200 includes 8reserved bits indicated by “R,” a format field describing the addresslength (32 or 64 bits) and whether the packet is a request orcompletion, a traffic class field (“TC”), a transaction layer packetdigest (“TD”), a poison bit (“EP”), attributes (“Attr”), address type(AT), length in 4 byte increments, a requester ID 204 and a tag field210 which together comprise the transaction ID, and last and firstdoubleword byte enables (Last DW BE and 1st DW BE). The requester IDfield 204 includes information used by the routing mechanisms of thecomputer system 100 to identify the source of the request and to route aresponse, if provided, to the requester. The address field (206 and 208)comprises a set of high order bits 206 and a set of low order bits 208.Taken together the address field (206 and 208) indicates either theaddress of the PCIe adapter 110 or I/O expansion adapter 111 to whichthe request is directed for a downbound transaction, or the systemmemory address of the system memory 104 for an upbound transaction.

The completion packet generally comprises a header and payload (notshown) segment. FIG. 2 b depicts a standard PCIe completion header 250.The first bytes 252 of the PCIe completion header 250 includes 9reserved bits indicated by “R,” a Format field describing the addresslength (32 or 64 bits) and whether the packet is a request orcompletion, a traffic class field (“TC”), a transaction layer packetdigest (“TD”), a poison bit (“EP”), attributes (Attr), length in 4 byteincrements, a completer ID 254, completion status 258, byte countmodified 260 (“BCM”), a byte count 262, a requester ID 256 and tag field264 which comprises the transaction ID of the request, and the low orderaddress 268 indicating the starting point of the payload data. Thecompleter ID field 254 is the identification of the PCIe adapter 110 orI/O expansion adapter 111 or host that performed the completion. Therequester ID 256 and Tag 264 of the PCIe completion header 250 containsthe requester ID 204 and Tag 210 of the PCIe request header 200 to matchmemory completions to their corresponding memory requests. The requesterID 256 is used to route the completion information back to theoriginator of the memory request. The PCIe completion header 250 alsoincludes a completion status field 258 for indicating if the request wascompleted successfully or if an error occurred while the adapter (PCIeadapter 110 or I/O expansion adapter 111) or host was processing therequest.

Turning now to FIG. 3, an exemplary embodiment of the downboundexpansion logic 128 (part of I/O expansion logic 122) depicted in FIG. 1for interpreting and transmitting I/O expansion operations from the hostbus 120 to the PCIe bus 126 will be described. I/O expansion operationsinclude a plurality of memory requests (also referred to herein as“downbound requests”) and a plurality of responses (also referred toherein as “downbound responses”). The host bus 120 connects the hostsystem 124 to the I/O hub 112 of FIG. 1 and provides transport servicesfor directing requests and responses from the host system 124 to thePCIe adapters 110 and the I/O expansion adapters 111. The I/O expansionadapters 111 operate in a communication format which is incompatible(i.e. not supported) with the PCIe standard format used by the PCIe bus126, therefore, transformation logic 132 executes within the I/Oexpansion adapters 111 to enable communication to the PCIe bus 126. Thetransformation logic 132 transforms (i.e. reformats) requests andresponses in the I/O expansion adapter 111 to a format that can beinterpreted by the PCIe bus 126. In an exemplary embodiment, thetransformation logic 132 executes in logic circuits on the I/O expansionadapter 111. In an alternate embodiment, the transformation logic 132executes on one or more specialized hardware circuits communicativelycoupled to the I/O expansion adapters 111 and the PCIe bus 126. In anadditional alternate embodiment, the transformation logic 132 executesas software in the I/O expansion adapter 111. Although downboundrequests and downbound responses are operations that are both initiatedby the host system 124, different process flows in the downboundexpansion logic 128 are used to process each of the operations.

In an exemplary embodiment, a downbound request is placed onto the hostbus 120. After a downbound request is placed on the host bus 120, theI/O hub 112 of FIG. 1 collects the downbound request and passes it tothe downbound expansion logic 128. The downbound expansion logic 128provides routing and transformation services based on informationcontained in the memory request. A downbound I/O expansion vector 304 isused to determine if the downbound request is being sent to one of theI/O expansion adapters 111 of FIG. 1. The downbound I/O expansion vector304 retrieves information from a header of the downbound request, andusing bit select logic 306 determines the destination of the downboundrequest. A cache inhibited (CI) load/store control 308 storesinformation related to downbound requests, such as a portion of the hostaddress indicating the target I/O expansion adapter 111 and an operationcode, if the host system 124 has indicated a response is required.

In an exemplary embodiment, a downbound request that is bound for one ofthe I/O expansion adapters 111 of FIG. 1 is transformed into a PCIecompatible downbound request by a multiplexor 312. In an additionalembodiment, the CI load/store control 308 sets the opcode in the headerof the memory request that is sent from the I/O hub 112 to the PCIe bus126, this data is used to process an upbound response at block 310 aswill be described in more detail in reference to FIG. 4.

In an exemplary embodiment, a downbound response is initiated from thehost system 124 in response to completing a request from one of the I/Oexpansion adapters 111. The downbound response is placed on the host bus120 and is collected by the I/O hub 112 and passed to the downboundexpansion logic 128. A DMA completion table 320, as depicted in FIG. 3,contains records for all requests that are awaiting responses. In anexemplary embodiment the records in the DMA completion table 320 areupdated to include information required to forward the downboundresponse from the host system 124 to the I/O expansion adapter 111. Aresponse address table (RAT) 318 is used to lookup downbound responserouting information. The address information is stored for requests sentfrom the I/O expansion adapters 111 to the host bus 120 (also referredto herein as “upbound requests”) as they are processed, as will bedescribed in more detail below. The upbound processing logic transmitsthe address data to the RAT 318 at the appropriate processing step atblock 316 as will be described in more detail below in reference to FIG.4. Control logic 322 adds an operation code (also referred to herein as“opcode”) to the downbound response which is used by the I/O expansionadapters 111 to process the downbound response. In an exemplaryembodiment the downbound expansion logic 128 is implemented in hardwarecircuits in the I/O hub, however, it will be understood that inalternate embodiments the downbound expansion logic may be executed assoftware in the hub or as a combination of hardware and softwareexecuting on the hub or other logic circuits as is known in the art.

Turning now to FIG. 4, an exemplary embodiment of the upbound expansionlogic 130 (part of I/O expansion logic 122) depicted in FIG. 1 forinterpreting and transmitting I/O expansion operations from the PCIe bus126 to the host bus 120 will be described. These I/O expansionoperations include a plurality of requests (also referred to herein as“upbound requests”) and a plurality of responses (also referred toherein as “upbound completions”). Both upbound requests and upboundcompletions are initiated by one ore more of the I/O expansion adapters111. An upbound I/O expansion vector 422 is used to determine if theupbound request is being sent from one of the I/O expansion adapters111. The upbound I/O expansion vector 422 retrieves information from aheader of the upbound request, and using the bit select logic 424determines the source of the upbound request. Once the source of theupbound request is determined, the address routing information is storedin the RAT 318 of FIG. 3, by transporting the data to the RAT 318 atblock 416. A multiplexor 412 is used to extract the requester ID field204 from the PCIe request header 200 of FIG. 2 a from the upboundrequest. The requester ID field 204 bus number is passed to the RAT 318.The requester ID field 204 including the bus number, device number, andfunction number is passed from the multiplexor 412 to a requester IDcontent addressable memory (RID CAM) 414. The RID CAM 414 provides anindex into the device table 402. The device table 402 is used todetermine the virtual address of a particular function within the I/Oexpansion adapter 111 of FIG. 1 based on the requester ID field 204. Thedata extracted from the device table 402 is modified by a multiplexor410, and the output of the multiplexor 410 is used by a zone relocationtable 404 to determine the correct address and partition of the hostsystem 124 for which the request is to be sent. The operation code ofthe packet is processed by control logic 418 and is transformed into theappropriate I/O expansion operation code before being transmitted to thehost bus 120.

In an exemplary embodiment, the upbound completions are processed asdescribed above, however, the control logic 418 matches the upboundcompletion with a downbound request using data transmitted to it fromthe CI load/store control 308 at block 420 when the downbound requestwas processed as described above.

Turning now to FIG. 5, a detailed block diagram of an exemplaryembodiment of an upbound I/O expansion request processing flow will nowbe described. In an exemplary embodiment, the upbound I/O expansionrequest processing flow depicted in FIG. 5 executes in the I/O expansionlogic 122 of the I/O hub 112 and the transformation logic 132 of the I/Oexpansion adapter 111 of FIG. 1. The processing flow depicted in FIG. 5transforms an upbound request (or upbound packet(s) of a transaction)into the format of the PCIe request header 200 of FIG. 2 a. At block502, one of the I/O expansion adapters 111 of FIG. 1 initiates a requestfor an operation to be executed on the host system 124 of FIG. 1 and thetransformation logic 132 creates a standard PCIe request including aPCIe request header 200.

At block 504, I/O expansion information from the request is embedded ina transformed PCIe request header, such as the transformed PCIe requestheader 600 depicted in FIG. 6. FIG. 6 depicts block diagram of atransformed PCIe request header that may be implemented by an exemplaryembodiment. The first 4 bytes of the PCIe request header 202 shown inFIG. 6 remain unchanged and function in the same way as described abovewith regard to FIG. 2 a. As shown in FIG. 6, the requester ID field 204of FIG. 2 a is replaced with two new fields, a request ID bus numberfield 602 and a zone ID field 604. The request ID bus number field 602identifies the I/O expansion adapter 111 from which the request wasreceived on the host system 124. The zone id field 604 is used toindicate a logical partition (not shown) of the host system 124, whichis used by the I/O expansion logic 122 to indicate which area of systemmemory the request is for. Each Logical Partition (LPAR) has itsseparate area of system memory, or zone. The high order bits of theaddress field 206 of FIG. 2 a, are replaced with a field to indicate tothe I/O expansion logic 122 that this request is a DMA write operationas opposed to an atomic or test & store operation which are alsotransmitted from the I/O expansion adapter 111 as posted memory writerequests. A key field 608 is used to protect unauthorized system memoryaccesses. The remaining bits including the high order bits of theaddress field 206 (field 610) are left unchanged. The low order bits ofthe address field 208 as well as the reserve bits 216 are leftunchanged. Although specific modifications have been described, it willbe understood that other fields or values in the request header could bemodified or added in alternate embodiments while still preserving thefunctions described above.

Returning now to block 506 of FIG. 5, once the PCIe request header hasbeen formatted to embed the I/O expansion transaction information into aPCIe formatted request, the request, including the transformed PCIerequest header 600, is sent to the host system 124 via the I/O hub 112.At block 508, the I/O hub 112 uses the PCIe bus number 602 of FIG. 6from the transformed I/O PCIe request header 600 as an index into theupbound I/O expansion vector 422 to determine if the request is from anI/O expansion adapter 111. If the bit corresponding to the bus number ison, the request is from an I/O expansion adapter 111. If the bit is off,the request is from a PCIe adapter 110. If the request is from a PCIeadapter 110, the fields in the PCIe header are interpreted as a normalPCIe request header and processed accordingly at block 514. If therequest is from an I/O expansion adapter 111, the zone ID field 604identifies the memory zone of the LPAR (not shown), and the zone IDfield 604 is used to relocate the system memory address throughmultiplexor 410 and the zone relocation table 404. The resultingrelocated address is included in the host request. The key field 608 isa memory protection key and controls access to system memory. The key isincluded in the host request. The high order bits of the address field606 indicate to the I/O expansion logic 122 that this request is a DMAwrite operation as opposed to an atomic or test & store operation whichat block 510 the I/O hub 112 sends the request to the host system 124.If the operation is an atomic or test & store operation, furthermodifications to the header include lock bytes and opcodes.

Turning now to FIG. 7, a detailed block diagram of an exemplaryembodiment of an upbound I/O expansion response processing flow will nowbe described. In an exemplary embodiment, the upbound I/O expansionresponse processing flow depicted in FIG. 7 executes in the I/Oexpansion logic 122 of the I/O hub 112 and the transformation logic 132of the I/O expansion adapters 111 of FIG. 1 and transforms an upboundresponse into the format of the PCIe request header 200 of FIG. 2 a forI/O expansion transactions that require a response but for which a PCIeresponse is not supported (e.g., write requests). At block 702, the I/Oexpansion adapter 111 of FIG. 1 creates a response to a request that waspreviously sent by the host system 124 of FIG. 1. In an exemplaryembodiment, the response includes data such as, but not limited to arequestor identifier, and an operation code to match the response to thecorresponding request. At block 704 the I/O expansion adapter 111determines if the response is for a read or a write request. If theresponse is for a read request, the I/O expansion adapter 111 replaces aportion of the completer ID field 254 of FIG. 2 b with a response code(not shown) which is not defined by the PCI specification.

At block 706, if the response is for a posted memory write, I/Oexpansion information from the response is embedded in a transformedPCIe request header, such as the transformed PCIe request header 800depicted in FIG. 8. FIG. 8 depicts a block diagram of an exemplaryembodiment of a transformed PCIe request header containing an I/Oexpansion response. The first 4 bytes of the PCIe request header 200 ofFIG. 2 a remain unchanged and function in the same way as describedabove with regard to FIG. 2 a. As shown in FIG. 8, the requester IDfield 204 of FIG. 2 a is replaced with two new fields, a request ID busnumber field 802 and an operation code field 804. The request ID busnumber field 802 is the identification information of the I/O expansionadapter 111 that initiated the request. The operation code field 804, isused to indicate the type of request that was completed by the I/Oexpansion adapter 111. Three of the high order bits of the address field206 of FIG. 2 a, are replaced with bits indicating that the response isto update the CI load/store control 308 of FIG. 3 with an indicatorflagging the transaction as complete. The low order bits of the addressfield 208 of FIG. 2 a are modified to include a response code field 814for indicating the status of the completed request, the write tag 816from the request for which this response is being generated, and a setof filler bits 818. The reserved bits 216 of FIG. 2 a remains unchanged.Although specific modifications have been described, it will beunderstood that other fields or values in the request header could bemodified or added in alternate embodiments while still preserving thefunctions described above.

Returning now to block 708 of FIG. 7, once the PCIe request header hasbeen formatted to embed the response information into a PCIe formattedrequest, the formatted request, including the transformed PCIe requestheader 800, is sent to the host system 124 via the I/O hub 112. At block710, the I/O hub 112 receives the PCIe request and transforms it to aresponse format supported by the host system 124. The host systemresponse includes a host tag and a return code. If the response isdetermined to be a memory read, the payload data (i.e. the data that hasbeen read) is also included. At block 712 the I/O hub 112 sends theresponse to the host system 124.

Technical effects and benefits include enabling non-PCIe compatible I/Oadapters to be implemented on a PCIe architecture along with PCIecompatible adapters without requiring modifications to the PCIe bus andPCIe switch mechanisms.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

As described above, embodiments can be embodied in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. In exemplary embodiments, the invention is embodied incomputer program code executed by one or more network elements.Embodiments include a computer program product on a computer usablemedium with computer program code logic containing instructions embodiedin tangible media as an article of manufacture. Exemplary articles ofmanufacture for computer usable medium may include floppy diskettes,CD-ROMs, hard drives, universal serial bus (USB) flash drives, or anyother computer-readable storage medium, wherein, when the computerprogram code logic is loaded into and executed by a computer, thecomputer becomes an apparatus for practicing the invention. Embodimentsinclude computer program code logic, for example, whether stored in astorage medium, loaded into and/or executed by a computer, ortransmitted over some transmission medium, such as over electricalwiring or cabling, through fiber optics, or via electromagneticradiation, wherein, when the computer program code logic is loaded intoand executed by a computer, the computer becomes an apparatus forpracticing the invention. When implemented on a general-purposemicroprocessor, the computer program code logic segments configure themicroprocessor to create specific logic circuits.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

What is claimed is:
 1. A system for implementing non-standard I/Oadapters in a standardized input/output (I/O) architecture, the systemcomprising: an I/O adapter configured to communicatively couple to anI/O hub via an I/O bus, the I/O adapter configured to communicate in afirst protocol, the I/O bus configured to communicate in a secondprotocol different than the first protocol, and the system is configuredto perform: initiating a first request to perform an operation on a hostsystem, the first request formatted for the first protocol andcomprising data required to process the first request; creating a secondrequest based on the first request, the second request comprising aheader and formatted according to the second protocol, the creatingcomprising storing the data required to process the first request in theheader of the second request; and sending the second request to the hostsystem; and the I/O hub, wherein the system is further configured toperform: receiving the second request at the I/O hub; converting thesecond request from the second protocol to a third request, the thirdrequest formatted for the first protocol; and sending the third requestto the host system.
 2. The system of claim 1, wherein the I/O bus is aperipheral component interconnect express (PCIe) bus.
 3. The system ofclaim 1, wherein the first protocol is an I/O expansion protocol and thesecond protocol is PCIe.
 4. The system of claim 1, wherein the I/Oadapter comprises an I/O expansion adapter that shares the I/O bus withat least one PCIe adapter.
 5. The system of claim 1, wherein thereformatted request is in a format not supported by the I/O adapter andthe host system.
 6. A system for implementing non-standard input/output(I/O) adapters in a standardized I/O architecture, the systemcomprising: an I/O adapter configured to communicatively couple to anI/O hub via an I/O bus, the system configured to perform: receiving arequest from a requester to perform an operation on the I/O adapter, therequester requiring a completion status; performing the operationresulting in a response, the response comprising the completion status;generating a new request in accordance with a first protocol based onthe performing; modifying a header of the new request to include theresponse; and sending the new request as the completion status to therequester in accordance with a second protocol; and the I/O hub, whereinthe system is further configured to perform: receiving the new requestat the I/O hub; converting the new request into a second request, thesecond request in a format supported by the host system; and sending thesecond request to the host system.
 7. The system of claim 6, wherein theI/O bus is a PCIe bus.
 8. The system of claim 6, wherein the format ofthe response is an I/O expansion format.
 9. The system of claim 6,wherein the I/O adapter comprises an I/O expansion adapter, the I/Oexpansion adapter sharing the I/O bus with at least one PCIe adapter.10. The system of claim 6, wherein the new request is in a format notsupported by the I/O adapter and the host system.